A backup relationship may be established between a primary data storage system and a secondary data storage system to support redundant storage of data in case there is a need to recover lost data. Once the backup relationship is established, the primary data storage system is synchronized with the secondary data storage system such that data written to the primary data storage system is copied to the secondary data storage system. A data inconsistency may occur if data is accessed from the primary data storage system after being modified in the primary data storage system but before being modified in the secondary data storage system.
For example, suppose that the value A is written to location X in the primary data storage system; synchronization of location X fails; the value A is read from location X; a function of the value A is computed and the result (i.e., value B) is written to location Y in the primary data storage system; and synchronization of location Y succeeds. In such a scenario, data stored in the secondary data storage system is inconsistent. That is, the value B stored in location Y in the secondary data storage system is not the result of computing a function of the value A stored in location X in the secondary data storage system.